package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * TermPositions provides an interface for enumerating the &lt;document,
 * frequency, &lt;position&gt;* &gt; tuples for a term.
 * <p>
 * The document and frequency are the same as for a TermDocs. The positions
 * portion lists the ordinal positions of each occurrence of a term in a
 * document.
 * 
 * @see IndexReader#termPositions()
 */

public interface TermPositions extends TermDocs {
	/**
	 * Returns next position in the current document. It is an error to call
	 * this more than {@link #freq()} times without calling {@link #next()}
	 * <p>
	 * This is invalid until {@link #next()} is called for the first time.
	 */
	int nextPosition() throws IOException;

	/**
	 * Returns the length of the payload at the current term position. This is
	 * invalid until {@link #nextPosition()} is called for the first time.<br>
	 * 
	 * @return length of the current payload in number of bytes
	 */
	int getPayloadLength();

	/**
	 * Returns the payload data at the current term position. This is invalid
	 * until {@link #nextPosition()} is called for the first time. This method
	 * must not be called more than once after each call of
	 * {@link #nextPosition()}. However, payloads are loaded lazily, so if the
	 * payload data for the current position is not needed, this method may not
	 * be called at all for performance reasons.<br>
	 * 
	 * @param data
	 *            the array into which the data of this payload is to be stored,
	 *            if it is big enough; otherwise, a new byte[] array is
	 *            allocated for this purpose.
	 * @param offset
	 *            the offset in the array into which the data of this payload is
	 *            to be stored.
	 * @return a byte[] array containing the data of this payload
	 * @throws IOException
	 */
	byte[] getPayload(byte[] data, int offset) throws IOException;

	/**
	 * Checks if a payload can be loaded at this position.
	 * <p>
	 * Payloads can only be loaded once per call to {@link #nextPosition()}.
	 * 
	 * @return true if there is a payload available at this position that can be
	 *         loaded
	 */
	public boolean isPayloadAvailable();

}
